The present invention relates to a method for manufacturing a semiconductor device, in which an active layer is located on a supporting substrate with an insulating intermediate layer therebetween and a movable unit included in the active layer moves in relation to the supporting substrate in response to a force applied to the movable unit, which is correlated to a dynamic quantity to be measured by the device.
Such a device is proposed in JP-A-11-274142. As shown in FIG. 1, the proposed device 100 includes a substrate 1 that has a Silicon-On-Insulator (SOI) structure. The substrate 1 is composed of an active layer 1C, an insulating intermediate layer 1B, and a supporting substrate 1A. The active layer 1C and the supporting substrate 1A are made of silicon, and the insulating intermediate layer 1B is made of silicon oxide. The active layer 1C includes a movable unit 2. The movable unit 2 moves in relation to the supporting substrate 1A in response to a force applied to the movable unit 2. The force is correlated to a dynamic quantity to be measured by the device 100.
In the manufacturing process of the proposed device 100, a plurality of trenches 4 that extend through a silicon layer, from which the active layer 1C is formed, to the insulating intermediate layer 1B are formed by dry etching the silicon layer. Then, the sidewalls defining the trenches 4 are dry etched at the portions adjacent to the bottoms of the trenches 4 with a charge building up on the surface of the insulating layer 1B. The charge changes the trajectory angle of the etching ions, so the etching ions strike the sidewalls and locally etch the sidewalls defining the trenches 4 at the portions adjacent to the bottoms of the trenches to complete the movable unit 2.
However, according to the study conducted by the inventor of the present invention, when the movable unit 2 is completed by locally etching the sidewalls defining the trenches 4, jagged protrusions 3 are occasionally formed at a reverse side of the movable unit 2, at which the movable unit 2 face the insulating layer 1B. The local etching of the sidewalls proceeds while what is called polymer, which is a protection film used for anisotropically etching a layer to be etched, is unevenly deposited on the reverse side of the movable unit 2, which is formed by the local etching. As a result, the reverse side is unevenly protected against the etching ions deflected by the charge built up on the insulator layer 1B. Therefore, the reverse side is unevenly etched to form the jagged protrusions 3.
If the jagged protrusions 3 are formed on the reverse side, the space between the movable unit 2 and the insulator layer 1B may be narrowed or the jagged protrusions 3 may break and plug the gap between the movable unit 2 and the insulator layer 1B. In that case, the movable unit 2 is prevented from moving in response to a force applied to the movable unit 2, and it becomes impossible to measure the force that is correlated to a dynamic quantity by the device 100.
The present invention has been made in view of the above aspects with an object to prevent jagged protrusions from being formed on the reverse side of a movable unit of a semiconductor device, in which an active layer is located on a supporting substrate with an insulating intermediate layer therebetween and the movable unit moves in relation to the supporting substrate in response to a force applied to the movable unit, which is correlated to a dynamic quantity to be measured by the device.
To achieve the above object, according to the present invention, a method for manufacturing a semiconductor device includes a step of forming an SOI substrate that includes a semiconductor substrate, an insulating layer, and a semiconductor layer such that the insulating layer is located between the semiconductor layer and the semiconductor substrate. The method further includes a step of dry etching the semiconductor layer to form a trench that extends through the semiconductor layer to the insulating layer and a step of dry etching a sidewall defining the trench at a portion adjacent to a bottom of the trench to form a movable unit.
The later dry etching is implemented with a charge building up on a surface of the insulating layer that is exposed during the former dry etching such that etching ions strike and etch the portion of the sidewall. In addition, the later dry etching is implemented at an etching rate higher than that at which the former dry etching is implemented to reduce the deposition amount of a protection film that is deposited on a reverse side of the movable unit during the later dry etching.